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Intellectual disability is often poorly understood because its effects vary greatly among those who have it. Many people with intellectual disability are mildly affected and may not be identified until later during school years. Individuals with intellectual disability may also have physical or emotional problems.

People with intellectual disability who have a very low intelligence quotient (IQ) have serious limitations in their ability to function. However, with early intervention and appropriate support, they can also lead satisfying lives. The goal of treating intellectual disability is to help children stay in the family and participate in community life. In most states in the United States, they are guaranteed education and other services.

What Is an Intellectual Disability?

Intellectual disability begins in childhood and is characterized by limitations in both intelligence and adaptive skills. The following three criteria must be met for a diagnosis of intellectual disability:

  • IQ below 75
  • Significant limitations exist in adaptive behaviors, such as self-care, socializing, and communicating
  • The disability begins before age 18
What Are the Causes?

Any condition that impairs development of the brain before birth, during birth, or during childhood can cause intellectual disability. The main causes can be categorized as follows:

Genetic Conditions

Genetic abnormalities may be inherited from parents or may be caused by environmental factors. There are many genetic diseases are associated with intellectual disability. Examples include:

  • Phenylketonuria (PKU)—Children born with this rare genetic disorder cannot metabolize phenylalanine (PHE), which is an amino acid found in food. Without proper treatment, PKU can lead to intellectual disability.
  • Down syndrome—In a normal fertilized egg, chromosomes exist in pairs. But, in the case of Down syndrome, there are three of chromosome 21.
  • Fragile X syndrome—This is caused by mutations of the FMR1 gene, the leading cause of inherited intellectual disability.
Problems During Pregnancy

Use of alcohol or drugs by a pregnant mother can cause intellectual disability. Smoking can increase the risk, as well. Other risks during pregnancy include:

  • Malnutrition
  • Certain environmental toxins such as lead
  • Illnesses of a mother during pregnancy that can be passed on to her infant, such as:
  • Preeclampsia
  • Prescription medications such as isotretinoin and phenytoin
Problems at Birth

Prematurity and low birth weight may sometimes lead to intellectual disability. However, other birth complications and conditions or physical stress in the newborn stage may injure an infant's brain.

Problems After Birth

Other conditions that can damage a child's brain and possibly lead to intellectual disability include:

In addition, poisoning from lead, mercury, carbon monoxide, and other environmental toxins can cause permanent damage to a child's brain and nervous system.

How Is an Intellectual Disability Diagnosed?

The American Association on Intellectual and Developmental Disabilities (AAIDD) has a process for diagnosing and classifying a person with intellectual disability. This process involves assessing the person's IQ and adaptive skills. Adaptive skills fall into three categories:

  • Conceptual skills—For example, can the person read and write? Does he or she understand concepts like time and money?
  • Social skills—Does the person follow rules? Does he or she have interpersonal skills? Can he or she solve social problems?
  • Practical skills—Can the person take care of his daily needs? Can he or she work, use money, and stay safe?
What Are the Treatment Options?

The best assistance for people with intellectual disability begins with diagnosis and help early in life. Treatment includes:

  • Early intervention
  • Special education
  • Family support
  • Case management
  • Job training
  • Transition services
  • Housing services

With enough education and support, many people with intellectual disability can learn to take care of their basic needs and to live in the community.

Can Intellectual Disabilities Be Prevented?

Newborn screening followed by proper treatment can prevent intellectual disability resulting from certain conditions. Examples include:

  • Phenylketonuria (PKU)
  • Congenital hypothyroidism

Vaccines can prevent certain infectious diseases that may lead to intellectual disability. Women who plan to become pregnant should be current on all recommended vaccinations, such as:

Other interventions that can reduce the risk of intellectual disability include:

  • Early and comprehensive prenatal care, including prenatal vitamins containing folate
  • Abstaining from alcohol, tobacco, and drugs during pregnancy

Many parents also choose to have certain tests done during pregnancy, including ultrasound, amniocentesis, chorionic villus sampling, and blood tests. These tests cannot prevent intellectual disability, but they can give parents more time to prepare for a child with intellectual disability.


American Association on Intellectual and Developmental Disabilities

Centers for Disease Control and Prevention


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Live, Work, Play


Intellectual disability. The ARC website. Available at: Accessed October 3, 2014.

Children with an intellectual disability. The American Academy of Child and Adolescent Psychiatry website. Available at: Updated October 2013. Accessed October 3, 2014.

Diagnostic adaptive behavior scale. American Association on Intellectual and Developmental Disabilities website. Available at: Accessed October 3, 2014.

Intellectual disability. The Arc website. Available at: Accessed October 3, 2014.

Intellectual disability. Kronkosky Charitable Foundation website. Available at: Published May 2009. Accessed October 3, 2014.

Intellectual disability. National Dissemination Center for Children With Disabilities website. Available at: Updated June 2014. Accessed October 3, 2014.

Intellectual disability. Merck website. Available at: Updated November 2013. Accessed October 3, 2014.

8/19/2014 DynaMed's Systematic Literature Surveillance Reilly C, Atkinson P, et al. Neurobehavioral comorbidities in children with active epilepsy: a population-based study. Pediatrics. 2014;133(6):e1586-1593.

Last reviewed August 2014 by Michael Woods, MD

Please be aware that this information is provided to supplement the care provided by your physician. It is neither intended nor implied to be a substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with any questions you may have regarding a medical condition.

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